[PATCH] x86/mm: compile out __set_fixmap_x() when not needed

[Jan Beulich <jbeulich@xxxxxxxx>]

Only HYPERV_GUEST has a need for an executable fixmap, so with that option
unset __set_fixmap_x() (and l1_fixmap_x[] in turn) is unreachable. Address
this Misra rule 2.1 violation by introduction ofa new FIXMAP_X Kconfig
setting.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
Why is __set_fixmap_x() not found by Eclair as a rule 2.1 violation in the
x86_64-amd job?

--- a/xen/arch/x86/Kconfig
+++ b/xen/arch/x86/Kconfig
@@ -269,6 +269,9 @@ config MCE_NONFATAL
 config GUEST
        bool
 
+config FIXMAP_X
+       bool
+
 config XEN_GUEST
        bool "Xen Guest"
        select GUEST
@@ -309,6 +312,7 @@ config PV_SHIM_EXCLUSIVE
 
 config HYPERV_GUEST
        bool "Hyper-V Guest"
+       select FIXMAP_X
        select GUEST
        help
          Support for Xen detecting when it is running under Hyper-V.
--- a/xen/arch/x86/boot/x86_64.S
+++ b/xen/arch/x86/boot/x86_64.S
@@ -142,13 +142,13 @@ END(l2_directmap)
 
 /*
  * L2 mapping the Xen text/data/bss region, constructed dynamically.
- * Executable fixmap is hooked up statically.
+ * Executable fixmap, when in use, is hooked up statically.
  * Uses 1x 4k page.
  */
 DATA(l2_xenmap, PAGE_SIZE)
         idx = 0
         .rept L2_PAGETABLE_ENTRIES
-        .if idx == l2_table_offset(FIXADDR_X_TOP - 1)
+        .if IS_ENABLED(CONFIG_FIXMAP_X) && idx == 
l2_table_offset(FIXADDR_X_TOP - 1)
         .quad sym_offs(l1_fixmap_x) + __PAGE_HYPERVISOR
         .else
         .quad 0
--- a/xen/arch/x86/include/asm/fixmap.h
+++ b/xen/arch/x86/include/asm/fixmap.h
@@ -95,6 +95,8 @@ static inline unsigned long virt_to_fix(
     return __virt_to_fix(vaddr);
 }
 
+#ifdef CONFIG_FIXMAP_X
+
 enum fixed_addresses_x {
     /* Index 0 is reserved since fix_x_to_virt(0) == FIXADDR_X_TOP. */
     FIX_X_RESERVED,
@@ -118,6 +120,12 @@ extern void __set_fixmap_x(
 #define __fix_x_to_virt(x) (FIXADDR_X_TOP - ((x) << PAGE_SHIFT))
 #define fix_x_to_virt(x)   ((void *)__fix_x_to_virt(x))
 
+#else /* !CONFIG_FIXMAP_X */
+
+#define FIXADDR_X_SIZE  0
+
+#endif /* CONFIG_FIXMAP_X */
+
 #endif /* __ASSEMBLER__ */
 
 #endif
--- a/xen/arch/x86/mm.c
+++ b/xen/arch/x86/mm.c
@@ -147,8 +147,6 @@
 /* Mapping of the fixmap space needed early. */
 l1_pgentry_t __section(".bss.page_aligned") __aligned(PAGE_SIZE)
     l1_fixmap[L1_PAGETABLE_ENTRIES];
-l1_pgentry_t __section(".bss.page_aligned") __aligned(PAGE_SIZE)
-    l1_fixmap_x[L1_PAGETABLE_ENTRIES]; /* SAF-1-safe */
 
 bool __read_mostly machine_to_phys_mapping_valid;
 
@@ -6180,6 +6178,11 @@ void __set_fixmap(
     map_pages_to_xen(__fix_to_virt(idx), _mfn(mfn), 1, flags);
 }
 
+#ifdef CONFIG_FIXMAP_X
+
+l1_pgentry_t __section(".bss.page_aligned") __aligned(PAGE_SIZE)
+    l1_fixmap_x[L1_PAGETABLE_ENTRIES]; /* SAF-1-safe */
+
 void __set_fixmap_x(
     enum fixed_addresses_x idx, unsigned long mfn, unsigned long flags)
 {
@@ -6187,6 +6190,8 @@ void __set_fixmap_x(
     map_pages_to_xen(__fix_x_to_virt(idx), _mfn(mfn), 1, flags);
 }
 
+#endif /* CONFIG_FIXMAP_X */
+
 void *__init arch_vmap_virt_end(void)
 {
     return fix_to_virt(__end_of_fixed_addresses);